[Effects of interviews during body weight checks in general population surveys].

While surveying actually measured body weight is largely impractical in national surveys, self-reported weight is a simple and inexpensive method of collecting data. Previous research shows that data on reported body weight are falsified by systematic mis-reporting. This bias is said to be the consequence of the sensitive nature of information on body weight. Numerous studies on survey response suggest that certain modes of data collection are more conducive than others for probing sensitive information. This paper investigates the effect of the anonymous interviews, characteristics of the interviewer and respondents' familiarity with the survey, as factors that may impinge on reported body weight. Findings of this paper show that refusals to state the body weight are rare. Moreover, characteristics of interviewers account for only a small fraction of the variance in reported body weight. Yet the hypothesis that the absence of an interviewer in self-administered interviews increases reported body weight can be confirmed. This interview effect, however, occurred in men only. On average, male respondents in anonymous interview settings report on a body weight which is 1 kg more than they would report in other settings. The repeated participation of respondents in the Socio-Economic Panel Study (SOEP) increases their reported body weight accuracy which suggests a positive panel effect on respondents' willingness to disclose sensitive information.